Stent graft tapered spring

ABSTRACT

A stent graft includes a stent graft material of cylindrical shape and tapered stent springs coupled to the stent graft material. Each stent spring includes a first stent cell and a second stent cell contiguous with the first stent cell. The first stent cell and the second stent cell are coupled. The second stent cell of each tapered stent spring is smaller than the first stent cell thereby defining a tapered shape to the tapered stent springs. The stent graft is placed in a curved segment of a tortuous body lumen and rotationally positioned such that the smallest stent cell of each tapered stent spring is placed at an inside radius of the curved segment.

RELATED APPLICATIONS

This application is a division of and claims the benefit of U.S. patentapplication Ser. No. 10/423,163 filed Apr. 24, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to endoluminal structures. Moreparticularly, the present invention relates to endoluminal stent graftsfor use in curved body lumens.

2. Description of the Related Art

A conventional stent graft typically includes a radially expandablestent, formed from a plurality of uniform annular stent springs, and acylindrical shape graft material to which the stent springs are coupled.Stent grafts are well known for use in reinforcing or holding open theinterior wall of a generally tubular shape human vascular and other bodylumen.

At deployment, after percutaneous insertion and transluminal transportto the point of use within a damaged or diseased body lumen, e.g., ananeurysmal artery, the stent graft is radially expanded. A stent graftis self-expandable or expandable by application of pressure appliedoutwardly to the interior portion of the stent graft. After deployment,the stent graft should be somewhat rigid to provide sufficient supportto the body lumen.

FIG. 1A is a plan view of stent graft 1, according to the prior art,deployed within a substantially linear segment 10 of a body lumen 6.Stent graft 1 includes a plurality of closely spaced uniform stentsprings 2, each formed from a plurality of identical, coupled stentcells 4 into an annular shaped ring around a cylindrical shape stentgraft material 3. Within linear segment 10 of body lumen 6, stent graft1 experienced little or no axial bending force since linear segment 10of body lumen 6 generally comported with the cylindrical shape of stentgraft 1.

However, human luminal systems are tortuous by nature. FIG. 1B is a planview of stent graft 1, according to the prior art, deployed within acurved segment 11 of body lumen 6. As shown, curved segment 11 includesan interior radius 12.

Within curved segment 11, stent graft 1 is subject to a bending forceimposed by curved segment 11 of body lumen 6. Thus, after deployment ina tortuous body lumen, conventional stent grafts were often subjected tosignificant axial bending and flexing.

It was necessary to limit the amount of axial bending allowed in adeployed stent graft to avoid stent cell overlap at inside radius 12 ofcurved segment 11 of body lumen 6. Stent cell overlap caused binding orkinking of the stent graft 1 resulting in restriction of flow throughthe body lumen. Accordingly, the use of conventional stent grafts waslimited to certain applications that avoided damage to or destruction ofthe stent graft from excessive axial bending.

SUMMARY OF THE INVENTION

A stent graft includes a stent graft material of cylindrical shape andtapered stent springs coupled to the stent graft material. Each taperedstent spring includes a first stent cell and second stent cellcontiguous with the first stent cell, wherein the second stent cell iscoupled to the first stent cell, and further wherein the second stentcell is smaller than the first stent cell. In one embodiment, each stentcell is open and defines a serpentine shape. In another embodiment, eachstent cell is closed and each stent cell defines a diamond shape.

When properly positioned rotationally within a tortuous body lumen suchthat the smallest stent cells are placed along the inside radius of acurved segment of the tortuous body lumen, the tapered stent springsprovide axial flexibility to the stent graft in at least one direction.Thus, the stent graft easily conforms to the curved segment of thetortuous body lumen while maintaining support for the lumen at thecurved segment.

Accordingly, use of the stent graft avoids restriction of flow throughthe body lumen resulting from binding or kinking of the stent graft atcurved segments of the body lumen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a stent graft, according to the prior art,deployed within a substantially linear segment of a body lumen;

FIG. 1B is a plan view of a stent graft, according to the prior art,deployed within a curved segment of a body lumen;

FIG. 2A is a plan view of a bent stent graft, deployed within an aorticarch, in one embodiment according to the present invention;

FIG. 2B is a plan view of a stent graft, before deployment, in oneembodiment according to the present invention;

FIG. 2C is a partial cutaway plan view of an artery system containing adeployed stent graft in one embodiment according to the presentinvention;

FIG. 3 is a flat layout view of an individual tapered stent spring ofthe stent graft of FIGS. 2B and 2C;

FIG. 4 is a flat layout view of an individual tapered stent spring ofthe stent graft of FIG. 2A;

FIG. 5A is an enlarged view of the region V of FIG. 2B of stent graft200 before deployment; and

FIG. 5B is an enlarged view of the region V of FIG. 2C of the stentgraft deployed in a first curved segment of the artery system.

Common reference numerals are used throughout the drawings and detaileddescription to indicate like elements.

DETAILED DESCRIPTION

Stent graft 100 (FIG. 2A) includes a plurality of spaced apart taperedstent springs 102 coupled to a cylindrical shape stent graft material103. A tortuous body lumen, such as an artery system 106, in which stentgraft 100 is deployed, includes a curved segment, e.g., athoracoabdominal aortic arch 107, which is diseased or damaged and whichrequires endoluminal prosthetic support. Thus, stent graft 100 ispercutaneously inserted into artery system 106, transportedtransluminally to aortic arch 107, and deployed to support aortic arch107.

As shown, in one embodiment, stent graft material 103 may define one ormore perimeter openings 105, (fenstrations), that allow fluid flowthrough perimeter openings 105, out of stent graft 100, into othersegments (not shown) of artery system 106.

Tapered stent springs 102 provide axial flexibility to stent graft 100in at least one direction. Accordingly, stent graft 100 easily conformsto the curved shape of aortic arch 107 of artery system 106 whilemaintaining support for aortic arch 107. Use of stent graft 100 avoidsoverlap of stent cells 104 at an inside radius 112 of aortic arch 107and restriction of blood flow through artery system 106 resulting frombinding or kinking of stent graft 100 at aortic arch 107.

As discussed more fully below, tapered stent springs 102 are integraland define a wave-like, serpentine shape. Tapered stent springs 102include a plurality of open, i.e., with a broken incomplete perimeter,stent cells 104, including first stent cell 104A and second stent cell104B contiguous with first stent cell 104A. The serpentine shape oftapered stent springs, according to alternate embodiments, may, forexample, be zigzagged or stepped.

Contiguous stent cells, such as stent cells 104A and 104B whilesimilarly shaped, vary in size. In addition, as also discussed morefully below, tapered stent springs 102 include smallest stent cells104S, in which stent cell size within a particular stent spring 102 isminimum.

Although stent cells of a particular shape are described above, in lightof this disclosure, it is understood that tapered stent springs mayinclude stent cells of other shapes. For example, in FIGS. 2B, 2C, and3, tapered stent springs 202 include a plurality of diamond shape stentcells 204. More particularly, FIG. 2B is a plan view of stent graft 200,before deployment in artery system 206 (FIG. 2C). As shown, stent graft200 includes a central axis L.

Adjacent tapered stent springs 202, such as first tapered stent spring202A and second tapered stent spring 202B, of stent graft 200 are spacedapart and coupled, e.g., sewn, to cylindrical shape stent graft material203 (FIG. 2C) with sutures (not shown). Tapered stent springs 202 formindependent annular rings around cylindrical shape stent graft material203.

In one embodiment, cylindrical shape stent graft material 203 is insidetapered stent springs 202. In another embodiment, stent graft material203 is outside tapered stent springs 202.

FIG. 3 is a view an individual tapered stent spring 202 of stent graft200 of FIGS. 2B and 2C, opened up and shown in a flat layout view of onecylindrical element. Although shown in flat layout view, as should bereadily apparent to one skilled in the art in view of this disclosure,tapered stent spring 202 (tapered from one side of the stent graft to alocation 180 degrees opposing on the other side) forms an annulus in itsfinal configuration.

Referring to FIGS. 2B and 3 together, tapered stent spring 202 includesa plurality of stent cells 204, including a first stent cell 204A and asecond stent cell 204B contiguous with first stent cell 204A. Firststent cell 204A is directly coupled to second stent cell 204B to form apart of tapered stent spring 202. In a similar manner, subsequent stentcells 204 are coupled with their respective contiguous stent cells 204thus forming tapered stent spring 202.

Stent cells 204 are closed, i.e., form a structure with an unbrokenperimeter, and are diamond shape. Further, stent cells 204 includeupper, e.g., first, apexes 312 and lower, e.g., second, apexes 314 (FIG.3). Contiguous stent cells 204, such as stent cell 204A and stent cell204B, are directly coupled at lower apexes 314 and abutting upper apexes312 of contiguous stent cells 204.

Illustratively, first stent cell 204A includes an upper apex 312A andlower apex 314A. Similarly, contiguous second stent cell 204B includesan upper apex 312B and a lower apex 314B. Lower apex 314A of firsttapered stent cell 204A abuts and is directly coupled to upper apex 312Bof second tapered stent cell 204B. In a similar manner, subsequent stentcells 204 are coupled at respective abutting apexes 312 and 314 thusforming tapered stent spring 202.

As noted above, stent cells 204 are closed and each forms a diamondshape. With reference to the diamond shape of stent cells 204, stentcells 204 have cell circumferential distances 324 between upper apexes312 and lower apexes 314 of stent cells 204. As used herein, acircumferential distance is the distance between two points on taperedstent spring 202, e.g., cell circumferential distance 324 between upperapex 312 and lower apex 314, along a circumference which is defined bythe annular shape of tapered stent spring 202 and which passes throughthe two points.

Contiguous stent cells 204, such as stent cell 204A and stent cell 204B,while similarly diamond shaped, vary in size. For example, cellcircumferential distance 324A, between upper apex 312A and lower apex314A, of first stent cell 204A is greater than cell circumferentialdistance 324B, between upper apex 312B and a lower apex 314B, of secondstent cell 204B. The cell circumferential distances 324 of contiguousstent cells 204 of tapered stent springs 202 vary in a similar mannerand so are not discussed further.

Also with reference to the diamond shape of stent cells 204, stent cells204 have left, e.g., third, apexes 315 and right, e.g., fourth, apexes317 and cell lateral distances 326 therebetween. As used herein, alateral distance is the distance between two points on tapered stentspring 202, for example left apex 315 and right apex 317, along alateral axis (not shown) at the circumference of tapered stent spring202, which is coplanar with and parallel to central axis L of stentgraft 200.

Illustratively, first stent cell 204A includes left apex 315A and rightapex 317A with a first cell lateral distance 326A therebetween. Secondstent cell 204B includes left apex 315B and right apex 317B with secondcell lateral distance 326B therebetween.

In a manner similar to the cell circumferential distances 324, firstcell lateral distance 326A of first stent cell 204A is greater thansecond cell lateral distance 326B of contiguous second stent cell 204B.The cell lateral distances 326 of all contiguous stent cells 204 oftapered stent springs 202 vary in a similar manner and so are notdiscussed further. In addition, as discussed more fully below, taperedstent springs 202 include smallest stent cells 204S, in which cellcircumferential distances 324 and cell lateral distances 326, withinrespective tapered stent springs 202, are minimum.

When viewed in flat layout view as in FIG. 3, tapered stent spring 202defines an imaginary tapered envelope 316 enclosing tapered stent spring202. In particular, left apexes 315 of stent cells 204 define a leftportion 316L of tapered envelope 316 and right apexes 317 of stent cells204 define a right portion 316R of tapered envelope 316.

Although stent cells of a diamond shape are described above, in light ofthis disclosure, it is understood that tapered stent springs may includestent cells of other shapes according to other embodiments. For example,as discussed above in reference to the embodiment of FIG. 2A, integral,wave-like, serpentine shape, tapered stent springs are formed from openstent cells.

More particularly, FIG. 4 is a view an individual tapered stent spring102 of stent graft 100 of FIG. 2A, depicted in a flat layout view forclarity of presentation. Although shown flat, as should be readilyapparent to one skilled in the art in view of this disclosure, taperedstent spring 102 forms an annulus in its final configuration. Taperedstent spring 102 includes a plurality of stent cells 104, includingfirst stent cell 104A and second stent cell 104B contiguous with firststent cell 104A. Further, stent cells 104 include stent cell start,e.g., first, points 112, stent cell end, e.g., second, points 114, stentcell mid-, e.g., third, points 115, and stent cell peak, e.g., fourth,points 117.

As used herein, stent cell start point 112 is a first minima inflectionpoint along serpentine shape stent cell 104. Further, stent cell endpoint 114 is a second minima inflection point along serpentine shapestent cell 104, subsequent to start point 112. Still further, stent cellmid-point 115 is the point midway between, and co-linear with, stentcell start point 112 and stent cell end point 114. Finally, stent cellpeak point 117 is a maxima inflection point along serpentine shape stentcell 104, between stent cell start point 112 and stent cell end point114.

First stent cell 104A is integrally formed with second stent cell 104Bto form a part of tapered stent spring 102. In a similar manner,subsequent stent cells 104 are integrally formed with respectivecontiguous stent cells 104 thus forming annular shape tapered stentspring 102.

With reference to the serpentine shape of stent cell 104, stent cell 104has a cell circumferential distance 124 between stent cell start point112 and stent cell end point 114. Further, stent cell 104 has a stentcell lateral distance 126 between stent cell mid-point point 115 andstent cell peak point 117.

Contiguous stent cells, such as stent cells 104A and 104B whilesimilarly shaped, vary in size. For example, cell circumferentialdistance 124A of first stent cell 104A is greater than cellcircumferential distance 124B of second stent cell 104B. Similarly, celllateral distance 126A of first stent cell 104A is greater than celllateral distance 126B of second stent cell 104B. Cell circumferentialdistances 124 and cell lateral distances 126 of contiguous stent cells104 of tapered stent spring 102 vary in a similar manner and so are notdiscussed further. In addition, as discussed more fully below, taperedstent springs 102 include smallest stent cells 104S, in which cellcircumferential distances 124 and cell lateral distances 126 areminimum.

When viewed in flat plan view as in FIG. 4, tapered stent spring 102defines an imaginary tapered envelope 116 enclosing tapered stent spring102. In particular, stent cell midpoints 115 of stent cells 104 define aleft portion 116L of tapered envelope 116 and stent cell peak points 117of tapered stent springs 102 define a right portion 116R of taperedenvelope 116.

Referring now to FIGS. 5A and 5B, FIG. 5A is an enlarged view of theregion V of FIG. 2B of stent graft 200 before deployment and FIG. 5B isan enlarged view of the region V of FIG. 2C with stent graft 200deployed in first curved segment 211A of artery system 206. Stent graft200 includes first tapered stent spring 202A and adjacent second taperedstent spring 202B spaced apart on cylindrical stent graft material 203.

First tapered stent spring 202A includes a smallest stent cell 204S1 offirst tapered stent spring 202A. Further, first tapered stent spring202A defines a first imaginary tapered envelope 316A. Second taperedstent spring 202B includes a smallest stent cell 204S2 of second taperedstent spring 202B. Further, second tapered stent spring 202B defines asecond imaginary tapered envelope 316B.

Referring to FIGS. 2B, 5A and 5B together, as noted above, stent graft200 is well suited for deployment in artery system 206. As discussedmore fully below, prior to expansion stent graft 200 is rotationally,i.e., angularly about central axis L of stent graft 200, positionedwithin artery system 206 such that smallest stent cells 204S, such assmallest stent cell 204S1 of first tapered stent spring 202A andsmallest stent cell 204S2 of second tapered stent spring 202B, areplaced along a first curved segment inside radius 212A of first curvedsegment 211A of artery system 206. In one embodiment, radio opaquemarkers (not shown), well know to those of ordinary skill in the art,are used to rotationally orient stent graft 200 within artery system206.

Use of stent graft 200 that includes rotational positioning of smalleststent cells 204S of tapered stent springs 202 along first curved segmentinside radius 212A of first curved segment 211A of artery system 206allows deployed stent graft 200 to easily conform to first curvedsegment 211A of artery system 206 while maintaining support for arterysystem 206. Such rotational positioning of smallest stent cells 204Swithin artery system 206 avoids restriction of blood flow through arterysystem 206 resulting from binding or kinking of the stent graft at firstcurved segment 211A.

As shown in the FIGS. 5A and 5B, the spacing between adjacent stentsprings 202 changes after stent graft 200 is deployed at first curvedsegment 211A of artery system 206. Specifically, the spacing between aright portion 316R1 of imaginary tapered envelope 316A of first taperedstent spring 202A and a left portion 316L2 of imaginary tapered envelope316B of second tapered stent spring 202B changes at first curved segment206 before (FIG. 5A) and after (FIG. 5B) deployment of stent graft 200.

More particularly, the spacing between corresponding smallest stentcells 204S1 and 204S2 on adjacent tapered stent springs 202A and 202B,respectively, is different before and after deployment at first curvedsegment 211A of artery system 206. As used herein, stent cells 204 onadjacent tapered stent springs 202 are said to be corresponding whenstent cells 204 occupy the same relative positions, respectively, onadjacent tapered stent springs 202.

By way of illustration, before deployment (FIG. 5A), at the portion ofstent graft 200 intended for deployment at first curved segment 211A ofartery system 206, smallest stent cell 204S1 of first tapered stentspring 202A and corresponding smallest stent cell 204S2 of secondtapered stent spring 202B are spaced apart by a first spacing distance318-1 between right apex 317S1 of smallest stent cell 204S1 of firsttapered stent spring 202A and left apex 315S2 of corresponding smalleststent cell 204S2 of second tapered stent spring 202B.

Further, after deployment (FIG. 5B), at first curved segment 211A ofartery system 206, smallest stent cell 204S1 of first tapered stentspring 202A and corresponding smallest stent cell 204S2 of secondtapered stent spring 202B are spaced apart by a second spacing distance318-2 between right apex 317S1 of smallest stent cell 204A of firsttapered stent spring 202A and left apex 315S2 of corresponding smalleststent cell 204S2 of second tapered stent spring 202B.

Corresponding smallest stent cells 204S1 and 204S2 on adjacent stentsprings 202A and 202B, respectively, are spaced apart a relatively largefirst spacing distance 318-1 prior to deployment at first curved segment211A. Thus stent graft 200 may axially bend, to conform with firstcurved segment 211A, without overlap of corresponding smallest stentcells 204S1 and 204S2 positioned at first curved segment inside radius212A.

After deployment at first curved segment 211A, corresponding smalleststent cells 204S1 and 204S2 are pinched more closely together by thebending force imposed by first curved segment 211A. Thus, first spacingdistance 318-1 (FIG. 5A) is greater than second spacing distance 318-2(FIG. 5B), allowing stent graft 200 to conform to the curved shape ofartery system 206 at first curved segment 211A.

In another embodiment according to the present invention, stent graft200 may include multiple pluralities of tapered stent springs 202.Referring again to FIGS. 2B and 2C, the portion of stent graft 200deployed at first curved segment 211A of artery system 206 includes afirst plurality of tapered stent springs 209A (FIG. 2B) that providesaxial flexibility to stent graft 200 in one direction. Similarly, theportion of stent graft 200 deployed at a second curved segment 211B(FIG. 2C) of artery system 206 includes a second plurality of taperedstent springs 209B (FIG. 2B) that provides axial flexibility to stentgraft 200 in another direction.

Rotational positioning of smallest stent cells 204S of stent springs 202at first curved segment inside radius 212A provides axial flexibility tostent graft 200 in one direction. Rotational positioning of smalleststent cells 204S of stent springs 202 at second curved segment insideradius 212B provides axial flexibility to stent graft 200 in a seconddirection.

Since, axial flexibility may be provided to stent graft 200 in more thanone direction, stent graft 200 may be made to conform to body lumenscontaining compound curves. Thus, stent grafts for special applications,such as thoracic stent grafts at the arch level, abdominal stent graftsin the case of an angulated segment just distal to proximal neckfixation, or abdominal stent grafts at the iliac legs, are formed withembodiments of stent springs as discussed above.

Although stent springs forming a single stent graft is described above,in light of this disclosure, it is understood that stent springs formedaccording to the present invention may be utilized in forming abifurcated stent graft that includes a first stent graft and a secondstent graft for use in conjunction with the first stent graft.

This disclosure provides exemplary embodiments of the present invention.The scope of the present invention is not limited by these exemplaryembodiments. Numerous variations, whether explicitly provided for by thespecification or implied by the specification or not, such as variationsin structure, dimension, type of material and manufacturing process maybe implemented by one of skill in the art in view of this disclosure.

1. A method comprising: forming a first tapered stent spring comprisinga first stent cell and a second stent cell contiguous with said firststent cell, wherein said second stent cell of said first tapered stentspring is coupled to said first stent cell of said first tapered stentspring, and further wherein said second stent cell is smaller than saidfirst stent cell; forming a second tapered stent spring comprising afirst stent cell and a second stent cell contiguous with said firststent cell, wherein said second stent cell of said second tapered stentspring is coupled to said first stent cell of said second tapered stentspring, and further wherein said second stent cell is smaller than saidfirst stent cell; sewing said first tapered stent spring and said secondtapered stent spring to a stent graft material, wherein said firsttapered stent spring is spaced apart from said second tapered stentspring by a spacing distance.
 2. The method of claim 1 furthercomprising: rotationally positioning said first tapered stent springsuch that said second stent cell of said first tapered stent spring isplaced along an inside radius of a curved body lumen; and rotationallypositioning said second tapered stent spring such that said second stentcell of said second tapered stent spring is placed along said insideradius of said curved body lumen.
 3. The method of claim 2 furthercomprising subjecting said first tapered stent spring and said secondtapered stent spring to a bending force imposed by said curved bodylumen, wherein said spacing distance decreases.